The bi-layered polypyrrole (PPy) coatings were investigated for corrosion prevention of a carbon
steel. The inner layer was doped with the
Keggin structure anions of
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(PMo
12) and
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anions for stabilization of the passive oxide film at the metal–polymer interface, and the outer layer was doped with four organic anions of dihydroxynaphthalenedisulfonate (DHNDS), naphthalenedisulfonate (NDS), anthraquinonedisulfonate (AnqDS) or dodecylsulfate (DoS) for inhibition of the decomposition and release of PMo
12. The corrosion tests were performed in 3.5 wt. % NaCl aqueous solution. The corrosion resistance of the
steels covered by the bi-layered PPy films was found in the following order: PPy–PMo
12/PPy–DHNDS < PPy–PMo
12/PPy–NDS < PPy–PMo
12/AnqDS < PPy–PMo
12/PPy–DoS. The performance of corrosion protection related to the oxidized state of the polymer was discussed.